PHYSIOLOGY OF THE CHILD'S HEART The child's heart, in comparison with the rest of the body, is rela tively larger in size than that of the adult, and the lumina of the large arteries are relatively- greater. The younger the child, the more marked are these relations. A result of this is the fact that tbe blood pressure in the child's aortic system must be lower than in that of the adult. These conditions change with increasing relative narrowness of the arterial system toward puberty. While, in early infancy, the trans verse diameter of the large arteries (carotid and subclavian) is very great in comparison with the length of the body and the size of the heart, this decreases relatively very markedly from the seventh to the fifteenth year, when a decided growth in the size of the heart occurs; for at this time subclavian and carotid artmies are relatively smaller in size than they are at any other time during life (Beneke).
Expressed in figures, according to Baginsky, the volume of the heart is to the lumen of the ascending aorta of the child as 25 is to 20; just before puberty, as 140 is to 50; right after puberty, as 290 is to 61.
According to Beneke, the volume of the heart increases most markedly in tbe first year of life; from then to puberty it diminishes, in comparison with the size of the body, but still without losing its pre ponderance when compared with the other organs of the body. Ac cording to von Dusch, the size of the heart is relatively greatest in the newborn infant and drops during the first and second years of life rapidly to a minimum in comparison with the whole mass of the body, to increase again from the third to the seventh year.
In newborn infants the thickness of the muscle walls of the left and right ventricle differs only slightly (0.44 to 0.48 left, to 0.34 to 0.44 right, Bednar), while the weight of the left is to that of the right as 1.3 is to 1 (Engel), compared with 2.62 to 1 in the. adult. At six years the thickness of the wall of the right ventricle is not much greater than in the newborn (3 to 4 cm.), while that of tbe left ventricle reaches 4 to S cm.
Pericardial fat is absolutely absent in the newborn infant, is but scantily present during childhood and only develops in large amount after puberty- (W. Milner).
The ostia of the right side of the heart in childhood are wider than those of the left (see Bizot's table below).
The increase in growth of the size of the heart is not proportional to the growth of the body, hut hears a steadily decreasing ratio to it, aceord• ing to W. Muller, whose statements are founded upon 14S1 autopsies.
The volume of the heart of the newborn infant, taken absolutely, is about 23 c.c. and increases to about 100 c.c. by the seventh year. Between the seventh and fifteenth years the heart no longer increases so considerably in volutne, as it reaches on the average only 140 c.c. at the end of the fifteenth year, Thus the size of the heart is re/atively smallest just before puberty, and dining the development of puberty it again rapidly increases in bulk, The weight of the heart in the newborn infant is, according to K. von Vierordt, 0.S9 per cent. of the body weight (absolutely, on the average, 24 Gm.; according to Bcdnar, Gni.) as compared with 0.52 per cent. in the adult; e., considerably higher, in relation to the total body weight, than in the adult. This favorable relation diminishes gradually as the years of life increase. While the adult's total body weight at the end of his development has reached nineteen times the weight of the newborn infant, the heart has grown to be only- fifteen times as heavy as it was, so that the relation of the weight of the heart to that of the body is never again as favorable as it WRS in earliest infancy-.
It is a remarkable fact that the increase in the circumference of the heart, during its growth in the first years of life, is not proportional to its development in size and increase in weight. The circumference of the heart does not change much more in the first five years of life, in spite of the heart's increase in weight. This fact has been corroborated by the circumference estimations made by Bednar and Rilliet and Barthez.